Traditionally, class D amplifiers, which consist of two active devices that are alternately switched on and off, are very popular at audio frequencies. At RF frequencies, however, the output shunt capacitance of the transistor causes significant losses.
Alternatively, in class E amplifiers, the zero voltage switching operation mode is advantageous since it eliminates the shunt capacitance losses of class D amplifiers. Furthermore, optimal harmonic loading used in class F amplifiers leads in general to 10 to 20 percent enhancement in the power efficiency of continuously driven class AB and class B power amplifiers.
However, HBT technology has been used more widely, due to its high reliability and monolithic integration that make it suitable for satellite communication as well as wireless communication systems.
This is achieved by driving the two RF PAs with signals having constant envelope and time-varying phases. The phases are controlled in such a manner that the combination of the outputs of both PAs produces a system output with the desired amplitude and phase modulation.
This architecture is very sensitive to gain and phase imbalance between the two signal paths. In addition, it has limited dynamic range and the overall power efficiency is greatly affected by the type of RF combiner used and the statistics of the signal. The two constant-envelope signals generated to drive the nonlinear power amplifiers are given by. In such a case, and when the two paths are perfectly balanced, the output signal is a linear amplified replica of the input signal, and is given by.
Recent development and implementations of LINC-based architectures demonstrated the ability of this technique to provide very good linearity as well as significantly improved power efficiency for WiMAX applications, as shown in Figures 7 and 8. The amplitude information is then recovered by varying the bias of the power amplifier.
Polar modulation is well poised to enable development of multimode handsets for these multiple air interface standards. A generic block diagram of a polar modulation transmitter is shown in Figure 9. The delta-sigma modulator also offers a valuable potential solution to convert analog complex modulation information of envelope varying signals into digitally coded pulses to drive the switching mode amplifiers.
The filter is required to restore the analog signal before transmitting the information to the antenna. The quantization noise is spectrally shaped and normally falls outside of the bandpass. Prior to transmission toward the antenna, the original signal is restored by filtering the amplified RF digital signal with a high quality factor bandpass filter.
The bandpass filter is required to attenuate the out-of-band quantization noise and to suppress all higher harmonics. Hence, this transmitter topology has the potential to amplify digitally modulated signals with large peak-to-average-power ratios PAPR while maintaining high power efficiency and high linearity. These modulation schemes call for the development of spectrum and power efficient SRD transmitters that can support multiple air-interface standards. In this article, advanced power amplification architectures that have the potential to meet both the linearity and power efficiency requirements for emergent broadband wireless and satellite communications were presented.
Typical performance of digitally predistorted continuously driven power amplifiers and Doherty amplifiers have been discussed and their performance assessed.
The state-of-the-art in switching mode amplifier design was briefly presented. Finally, the principle and limitations of power amplification stages and transmitter architectures appropriate for use in switching mode power amplifiers were discussed. Jeonghyeon, Y. Jaehyok, J. Kim and K. Wangmyong, M. Miller and J. Sirois, S. Boumaiza, M. Helaoui, G.
Brassard and F. Larson, P. Asbeck and D. Galton and H. Bourdopoulos and T. Nagle, R. Husseini, A. Grebennikov, W. Ahmed and F. Conradi and J. Raab, P. Radio-Frequency Components. Synergistic design of DSP and power amplifiers for wireless communications. Co-design of digital signal-processing DSP algorithms and power-amplifier characteristics can lead to improved efficiency and linearity through a variety of strategies including: predistortion, DSP … Expand.
View 2 excerpts, references methods and background. Using a large-signal computer model for the MESFET with a modified harmonic balance technique the third-order intermodulation response of general amplifier circuits is found.
The effect of device, … Expand. A nonlinear equivalent circuit model for the GaAs FET has been developed based upon the small-signal device model and separate current measurements, including drain-gate avalanche current data.
The … Expand. Highly Influential. View 3 excerpts, references methods and background. The RF and microwave circuit design cookbook. Microwave Circuits and Circuit Elements.
Solid-State Devices. Diode Mixers. Diode Frequency Multipliers. Other Diode Applications. Active Mixers. FET Resistive Mixers. Active Frequency Multipliers. View 4 excerpts, references background. FET diode linearizer optimization for amplifier predistortion in digital radios. This letter presents the initial results of a study on a diode-based power amplifier PA linearization technique. View 3 excerpts, references background.
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